The invention relates to a hydrocracking process and is particularly concerned with the use of a hydrocracking catalyst containing a noble metal hydrogenation component and zeolite Beta to produce gasoline and/or middle distillates from feedstocks having a major proportion of components boiling above 500.degree. F.
Petroleum refiners often produce desirable products, such as gasoline and turbine fuel, by catalytically hydrocracking high boiling hydrocarbons into product hydrocarbons of lower average molecular weight and boiling point. Hydrocracking is generally accomplished by contacting, in an appropriate reactor vessel, a gas oil or other hydrocarbon feedstock with a suitable hydrocracking catalyst under appropriate conditions, including an elevated temperature and an elevated pressure and the presence of hydrogen, such that a hydrocarbon product is obtained containing a substantial portion of a desired product boiling in a specified range, as for example, a heavy gasoline boiling in the range of approximately 185.degree. to 420.degree. F.
Oftentimes, hydrocracking is performed in conjunction with hydrotreating, usually by a method referred to as "integral operation." In this process, the hydrocarbon feedstock, usually a gas oil containing a substantial proportion of components boiling above a desired end point, as for example, 420.degree. F. in the case of certain gasolines, is introduced into a catalytic hydrotreating zone wherein, in the presence of a suitable catalyst, such as a zeolite- or sieve-free, particulate catalyst comprising a Group VIII metal component and a Group VIB metal component on an amorphous, porous, inorganic, refractory oxide support most often composed of alumina, and under suitable conditions, including an elevated temperature (e.g., 400.degree. to 1000.degree. F.) and an elevated pressure (e.g., 100 to 5000 p.s.i.g.) and with hydrogen as a reactant, the organonitrogen components and the organosulfur components contained in the feedstock are converted to ammonia and hydrogen sulfide, respectively. Subsequently, the entire effluent removed from the hydrotreating zone is treated in a hydrocracking zone maintained under suitable conditions of elevated temperature, pressure, and hydrogen partial pressure, and containing a suitable hydrocracking catalyst, such that a substantial conversion of high boiling feed components to product components boiling below the desired end point is obtained. Usually, the hydrotreating and hydrocracking zones in integral operation are maintained in separate reactor vessels, but, on occasion, it may be advantageous to employ a single, downflow reactor vessel containing one or more upper beds of hydrotreating catalyst particles and one or more lower beds of hydrocracking particles. Examples of integral operation may be found in U.S. Pat. Nos. 3,132,087, 3,159,564, 3,655,551, and 4,040,944, all of which are herein incorporated by reference in their entireties.
In some integral operation refining processes, and especially those designed to produce gasoline from the heavier gas oils, a relatively high proportion of the product hydrocarbons obtained from integral operation will have a boiling point above the desired end point. For example, in the production of a gasoline product boiling in the C.sub.4 to 420.degree. F. range from a gas oil boiling entirely above 570.degree. F., it may often be the case that as much as 30 to 60 percent by volume of the products obtained from integral operation boil above 420.degree. F. If it is desired to convert these high boiling components to hydrocarbon components boiling below 420.degree. F., the petroleum refiner separates the 420.degree. F.+ high boiling components from the other products obtained in integral operation, usually after first removing ammonia by a water washing operation, a hydrogen-containing recycle gas by high pressure separation, and an H.sub.2 S-containing, C.sub.1 to C.sub.3 low BTU gas by low pressure separation. This 420.degree. F.+ boiling bottom fraction is then subjected t further hydrocracking, either by recycle to the hydrotreating or hydrocracking reactor in single stage operation or by introduction into a second hydrocracking zone wherein yet more conversion to the desired C.sub.4 to 420.degree. F. product takes place.
In the foregoing two stage process, the two hydrocracking reaction zones often contain hydrocracking catalysts of the same composition. One catalyst suitable for such use is disclosed as Catalyst A in Example 16 of U.S. Pat. Nos. 3,897,327 and 3,929,672, both of which are herein incorporated by reference in their entireties, which catalyst is comprised of a palladium-exchanged, steam-stabilized Y zeolite hydrocracking component. Although the catalysts used in the two hydrocracking reaction zones may have the same composition and the same catalytic properties, the hydrocracking conditions required in the second hydrocracking reaction zone are less severe than those required in the first. The reason for this is that ammonia is not present in the second hydrocracking reaction zone (due to water washing) whereas a significant amount of ammonia is present in the first hydrocracking zone. To account for the difference in operating conditions, it is believed that ammonia neutralizes or otherwise interferes with the acidity of the zeolite in the catalyst of the first reaction zone, thereby forcing the refiner to employ relatively severe conditions for operation, as for example, increased temperature. On the other hand, in the ammonia-deficient atmosphere of the second hydrocracking reaction zone, high conversions to the desired product are obtainable under relatively moderate conditions, often with an operating temperature about 100.degree. to 210.degree. F. lower than that required in the first hydrocracking reaction zone.
Further description of two-stage hydrocracking operations may be found in U.S. Pat. Nos. 4,429,053 and 4,857,169 herein incorporated by reference in their entireties, which patents provide process flow sheets for typical two-stage hydrocracking processes.
Although there exist several types of commercial hydrocracking catalysts which can be used effectively in single stage hydrocracking or in either the first, second or both stages of the above-discussed two-stage hydrocracking process, there is always a demand for new catalysts with superior overall activity, selectivity and stability for producing gasoline and/or other products via hydrocracking.